From what I have seen, you can use the French past participle, in addition to the present participle, as an adjective.

Par exemple:

En allant au boulot, j’ai vu votre voiture arrêtée au carrefour.

Ce sont des films amusants.

NOTE: The verbs must agree in gender and quantity

Il y avait des voitures arrêtées…

As I am not a native speaker, I can not say with certainty; however, I believe that your example (Le français parlé) would be acceptable. If you were to use it like you say you had been using it with the construnction qui est parlé then you would be using the passive voice.

According to the first example, that is appropriate:
here

I think you can also say à l’oral

À l’oral, le français risque d’être difficile à comprendre.